Monitoring system and method

ABSTRACT

A monitoring system includes one or more monitoring devices, positioned in sewer manholes, storm drains, etc., and a remote monitoring station that communicates wirelessly therewith. The monitoring device may be an integrated unit, including sensors, a two-way telemetry unit, a power supply, a processor, and supporting hardware, all located in an enclosed, waterproof housing. The monitoring device is placed within a manhole cavity to obtain depth (e.g., water level) measurements, images, and other data, and report the measurements back to the remote monitoring station, which analyzes the data and responds to alert messages when a dangerous water level is detected. An additional sensor may monitor the manhole cover for security purposes. A distributed mesh network of wireless nodes may be used to relay communications from the monitoring devices along alternative paths, through bridge nodes that may connect to a public wireless or cellular network.

RELATED APPLICATION INFORMATION

This application is a continuation-in-part of U.S. application Ser. No.11/303,435 filed Dec. 16, 2005, which is a continuation of U.S.application Ser. No. 10/091,852 filed Mar. 5, 2002, now U.S. Pat. No.7,002,481, both of which are hereby incorporated by reference as if setforth fully herein.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The field of the present invention relates generally to monitoringdevices and methods and, more particularly, to devices and methods formonitoring water depth and other aspects of sewers, storm drains,waterways, and the like.

2) Background

Most municipalities have a sanitary wastewater system, the purpose ofwhich is to collect and transport waste matter from the various drains,disposals and other sources within the community to a sewage treatmentplant or other such facility. Ideally, the waste matter is transportedvia the sanitary wastewater system without any spillage or leakagewhatsoever. However, sanitary wastewater systems can be enormous inscale, making their management and maintenance extremely challengingtasks. Even in smaller municipalities, managing and maintaining thelocal sanitary wastewater system can be difficult. Problems often arisefrom the demands placed upon these systems, which may be found in widelyvarying states of repair. Such demands generally include severe weatherconditions (such as heavy rains or freezing temperatures), accumulationof obstructive materials (e.g., grease, sediment, roots or otherdebris), and groundwater infiltration, to name a few. In addition,community growth, either industrial or residential, can lead toincreased strain on an existing sanitary wastewater system. When thewastewater collection system becomes taxed beyond capacity, manholeoverflows and/or backflow into residential areas may result.

The adverse conditions preceding an overflow (or other similar event)often exist over an extended period of time (usually several days orweeks), gradually worsen, and, if not detected and rectified, cause theinevitable result. During the time preceding such an overflow event,wastewater begins to accumulate in one or more localized areas withinthe collection system, until gradually the level of the wastewaterbecomes so high it breaches the nearest outlet—usually a manholeopening—or else backs upstream where further problems can be caused.

A sewer overflow can pose significant health hazards within a localcommunity. The cleanup operation can be costly, and an overflow canbring about an interruption in sewer service. Also, a sewer overflow canharm the local environment, and result in potential state and/or federalpenalties.

To reduce the likelihood of overflow and backflow events, it has beencommon practice to place flowmeters at various points within thewastewater collection system, thereby allowing the liquid flow withinthe system to be monitored. Often the flowmeters are placed at locationswhere access is convenient, such as in sewer manholes.

A variety of different flowmeters have been developed, a number of whichhave been used or proposed for use in a wastewater monitoring system.One common class of flowmeters has a “primary” element and a “secondary”element. The primary element is a restriction in a flow line thatinduces a differential pressure and/or level, and the secondary elementmeasures the differential pressure and/or level, converts themeasurements into a flow rate, and records the flow rate data. Weirs andflumes are some of the oldest and most common devices used as flowmeterprimary elements. More recently, flowmeters have been developed whichuse ultrasonic pulses to measure the liquid level, which is thenconverted into a flow rate.

A variety of drawbacks exist with conventional flowmeter monitoringsystems. First, many flowmeter installations are configured to providemanual reading of the flow data that has been acquired over time.Reading the flow meter data can be a burdensome task. Generally, a fieldworker is required to travel to the physical location of the manhole,pry off the manhole cover, descend into the manhole, and attempt tocollect the data from the secondary element of the installed flowmeter.Where numerous flowmeters are installed throughout a large municipalwastewater collection system, the task of collecting flow data from allof the flow meters can be a time-consuming, labor intensive (andtherefore expensive) process. In situations of sudden rainfall events orother circumstances, it can be very difficult for field workers tomonitor all of the flowmeters in the system, and a risk of overflowincreases.

In addition to the difficulty in obtaining flow data from flowmetersinstalled in a wastewater collection system, flowmeters can also beexpensive, and often require a high level of accuracy that can bedifficult to maintain over time. Inaccurate liquid flow measurements inthe context of a wastewater collection system can lead to serious oreven disastrous results. Flowmeters may also require periodic inspectionand cleaning, and can therefore be relatively expensive to maintain.

Various types of sewer monitoring systems have been developed orproposed to alleviate the need for manual data collection. One exampleis illustrated in U.S. Pat. No. 5,608,171 to Hunter et al. However,available sewer monitoring systems of the wireless variety generallyrequire devices that are expensive or require expensive components, canbe difficult to install or remove, and/or have limited functionality orcompatibility with other equipment.

It would therefore be advantageous to provide an improved technique formonitoring sewers, storm drains, waterways, and other such areas, toprevent overflows, facilitate maintenance, and improve informationavailable for municipal planning purposes.

SUMMARY OF THE INVENTION

The invention in one aspect is generally directed to systems and methodsfor monitoring water depth and other conditions of sewers, storm drains,waterways, and other such areas.

In one aspect, a monitoring device is placed within a manhole or othersuitable location for monitoring the buildup of water, sediment or othermaterials. The monitoring device preferably has a moisture-proof housingmade of a non-corrosive, water-resistant material, and includes internalelectrical circuitry (microprocessor, memory, etc.) for controlling thefunctions of the device. A sensor is oriented downward to obtain depthmeasurements at periodic intervals, and the measurements are stored inthe device until readout at a later time. At certain intervals, thestored measurements are transmitted wirelessly to a remote monitoringstation for evaluation and analysis.

In a preferred embodiment, the sample rate of the depth sensor and thefrequency of reporting to the remote monitoring station are adjustablethrough commands downloaded wirelessly from the remote monitoringstation. The monitoring device may also have internal alert modes whichare entered when the monitored water level passes specific thresholdvalues. Entry into a higher alert state may result in an increase insampling and/or reporting rates.

In one embodiment, the monitoring device has a housing with multiplelegs extending outwardly, for allowing the device to be mounted to theinterior walls of a manhole. The legs can be made of a flexible,bendable, or compressible material, or else can be adjusted in size byway of a rotatable screw member or a telescoping member. In anotherembodiment, the monitoring device has a cylindrical housing with aslightly wider cap or head, adapted for, e.g., drop-down insertion intoa hole in a manhole cover.

In various embodiments, additional external monitoring instruments maybe deployed in the manhole or other location where the monitoring deviceis situated, and connected to ports in the monitoring device, whichtransmits data received from the external monitoring instruments to theremote monitoring station. Also, the monitoring device may include asecond sensor, oriented upwards instead of downwards, to monitordisturbances to the manhole cover for security purposes.

A monitoring device as described herein may be used in the context of apreferred monitoring system, wherein a plurality of the monitoringdevices are positioned within different manholes or other locations overa geographic region, for monitoring water level or other conditionswithin the various manholes or other locations. In such a system, theremote monitoring station communicates wirelessly with the monitoringdevices and receives depth measurements at periodic intervals forprocessing and analysis. The sampling frequency and reporting frequencyof the monitoring devices are preferably programmably adjustable,individually for each of the monitoring devices, through wirelesscommands transmitted from the remote monitoring station to the variousmonitoring devices. The wireless communications may be facilitated usinga distributed mesh network of wireless nodes which provide foralternative communication paths from the various monitoring devices tothe remote monitoring station via one or more bridge nodes, which may bewireless in nature and may utilize a public wireless or cellularnetwork.

Further embodiments, variations and enhancements are also disclosedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a monitoring system according to apreferred embodiment as disclosed herein.

FIG. 2 is a diagram illustrating the positioning of a monitoring devicein a manhole.

FIG. 3 is a block diagram of a preferred monitoring device.

FIG. 4A is a diagram illustrating a monitoring device including legs formounting within a manhole.

FIG. 4B is a diagram illustrating a rotatable member for adjusting thelength of a leg for securing a monitoring device within a manholecavity.

FIG. 5 is a block diagram illustrating an alternative embodiment of amonitoring device.

FIGS. 6A and 6B are diagrams illustrating an example of one type ofantenna configuration for a monitoring device. FIG. 6A shows an obliqueview of the monitoring device with an antenna piece inserted in amanhole cover, while FIG. 6B shows a cross-sectional view thereof.

FIG. 7 is a diagram illustrating a monitoring device adapted fordrop-down insertion into a manhole.

FIG. 8 is a diagram illustrating an example of insertion of themonitoring device of FIG. 7 into a manhole.

FIG. 9 is a diagram illustrating an example of a drop-down monitoringdevice secured to a manhole lid by a retaining ring.

FIG. 10 is a block diagram illustrating another embodiment of amonitoring device, having a digital camera.

FIG. 11 is a block diagram of a portion of a monitoring system includingan end node and a street node.

FIG. 12A is a block diagram of an embodiment of a street node, and FIG.12B is a block diagram of an embodiment of a bridge node, such as acellular gateway node (or sky node).

FIG. 13 is a block diagram of a monitoring system utilizing a meshnetwork, according to a preferred embodiment as disclosed herein.

FIG. 14 is a diagram illustrating an example of communications within amesh network such as depicted in FIG. 13.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of a monitoring system 100 according to apreferred embodiment as disclosed herein. As illustrated in FIG. 1, themonitoring system 100 comprises a monitoring device 105 that can bepositioned in a location for monitoring a depth (e.g., water level),such as in a manhole 108, or else in a storm drain or another suitablelocation. In a preferred embodiment, the monitoring device 105 managesone or more data sensors and provides timing, control, data andprogramming storage, and wireless communication functions to allowremote monitoring of the activity and operation of the monitoring device105.

As further illustrated in FIG. 1, the monitoring device 105 preferablyincludes an antenna 106 for communicating wirelessly with remotestations. In the example shown in FIG. 1, the monitoring device 105communicates with a remote monitoring station 170 through a wirelessnetwork 150, which can be a cellular network or any other type ofwireless network. The wireless network 150 typically includes or isconnected to a plurality of base stations 152 for communicating withvarious fixed or mobile wireless devices, such as the monitoring device105.

While only one monitoring device 105 is shown in FIG. 1, it is to beunderstood that the monitoring system 100 can, and is likely to, includea significant number of monitoring devices identical or similarmonitoring device 105, in order to monitor various manholes, sewerpipes, and/or other water or runoff conduits in a local vicinity ormunicipality. Likewise, while only a single remote monitoring station170 is illustrated, additional remote monitoring stations may beincluded in the monitoring system 100, depending upon the size and scopeof the overall system 100. Thus, while the principles of operation maybe explained with respect to a single monitoring device 105 and remotemonitoring station 170, they may be extrapolated to any number ofmonitoring devices and remote monitoring stations in a given system. Inaddition, one or more of the monitoring devices may utilize a wiredconnection with the remote monitoring station 170 rather than a wirelessconnection, particularly where the monitoring system 100 is deployed inan area having some manholes or other locations outfitted withpre-existing wirelines.

In the example of FIG. 1, the remote monitoring station 170 includes aprocessing system 172 which may comprise, for example, one or morecomputers or processors for receiving data from the monitoring device(or devices) 105, processing the data, and transmitting commands orother information back to the monitoring device (or devices) 1-5. Theremote monitoring station 170 may include a database 174, local orremotely located, for storing data received from the monitoring device(or devices) 105. A user interface 173 allows operators oradministrators to review the stored data or interactively adjust theoperational parameters of the monitoring device (or devices) 105. Incertain implementations, the remote monitoring station 170 may processincoming data from the monitoring devices 105 and relay the data, usingany conventional means (such as electronic mail), to another site forstorage or evaluation.

Operation of the monitoring system 100 shown in FIG. 1 may be explainedwith reference to a preferred monitoring device 105, details of which,according to one example, are illustrated in FIG. 3. As shown in FIG. 3,a preferred monitoring device 300 includes housing 305 which ispreferably formed of a water-resistant, non-corrosive lightweightmaterial, such as plastic, fiberglass, or treated/sealed thin metal(e.g., aluminum). The housing 305 is preferably sealed so as to beeffectively watertight, although a swinging panel or access door (notshown) may be provided to allow replacement of the battery 322 orpossibly other components. The monitoring device 300 preferablycomprises a wireless communication unit 310 which is attached to anantenna 306, for carrying out wireless communication with a wirelessnetwork (such as network 150 shown in FIG. 1). The wirelesscommunication unit 310 preferably comprises at least a wirelesstransmitter but may also include a wireless receiver as well (or else beembodied as a wireless transceiver).

The monitoring device 300 preferably includes a processor 312 (which maycomprise, e.g., a microprocessor, microcomputer, or digital circuitry)for controlling the basic functions of the monitoring device 300,including, for example, instructions to transmit data via the wirelesscommunication unit 310, or interpretation of data received via thewireless communication unit 310. The processor 312 preferably includes(or is connected to) a non-volatile memory portion 314 for storingprogramming instructions for execution by the processor 312 and otherdata, and a volatile memory portion (e.g., random-access memory or RAM)315 for storing programmable operation parameters, and for storing depth(e.g., water level) measurements as needed.

The processor 312 may be connected to various clocks and/or timers 317for carrying out timing of certain events (e.g., timing of intervalsbetween samples or data transmissions), and may be connected to a sensor325 for measuring depth (e.g., water level). The sensor 325 ispreferably capable of taking distance measurements in conditions of verylow light as may be experienced when the device is installed in amanhole. The sensor 325 may, for example, be embodied as an ultrasonicsensor which uses the time delay of echoed sound waves to detect thedistance from the sensor 325 to the nearest solid object (e.g., watersurface). The sensor 325 may also, for example, utilize an electrostatictransducer for ultrasonic detection. Ultrasonic sensors utilizingelectrostatic transducers are known in the art and are manufactured, forexample, by SensComp, Inc. of Livornia, Mich., and others. Anelectrostatic transducer may be well suited for detecting soft objectsand ranging to targets at both near and far distances. The sensor 325may have a sensor window 326 affixed to the housing 305 of themonitoring device 300, for providing a viewpath 329 (illustrated as 107in FIG. 1) for the sensor 325.

The monitoring device 300 preferably draws operating energy from anin-unit, low-voltage battery 322, which supplies energy to the processor312, sensor 325, wireless communication unit 310, and any othercomponents as necessary. As indicated elsewhere herein, the sensorsampling rate and data transmission rate of the monitoring device 300are preferably kept to a minimum to prolong the life of the battery 322as much as possible.

The monitoring device 300 may include one or more input/output (I/O)ports 319, to which can optionally be connected to various peripheralmonitoring devices or instruments 320. Examples of peripheral monitoringdevices include, for example, external flowmeters, heavy metaldetectors, toxic gas detectors, and any other type of useful monitoringdevice. A peripheral monitoring device may also comprise a so-called“lab-on-a-chip,” in other words, a microchip consisting of, e.g.,interconnected fluid reservoirs and pathways that effectively duplicatethe function of valves and pumps capable of performing manipulationssuch as reagent dispensing and mixing, incubation/reaction, samplepartition, and analyte detection. The processor 312 may be configured toreceive input signals, via the I/O ports 319, from the variousperipheral monitoring devices 320, and to process the input signals,store the input signals in volatile memory 315, and/or convey the inputsignals, via the wireless communication unit 310, to the remotemonitoring station. The monitoring device 300 may identify the variousperipheral monitoring devices 320 by their particular I/O port number,by an equipment identification number or type number, or by any othersuitable means, so that the remote monitoring station can interpret thesource of readings or other information received from the monitoringdevice 300.

When not active, the various components of the monitoring device 300 arepreferably rendered inactive by, e.g., placing them in a “sleep” statewherein no or minimal power is consumed. For example, the sensor 325,processor 312, and wireless communication unit 310, and possibly othercomponents, may all be placed in an inactive state when no activity isnecessary, and awakened upon the occurrence of an event needingattention (for example, the timeout of a sampling or reporting intervalin a timer). At that point, power may be re-connected to the inactivecomponents as necessary. Operation in this manner may significantlypreserve battery life.

In operation, the monitoring device 300 takes periodic measurements ofdepth (e.g., water level) using the sensor 325, and stores the depthmeasurements in either the non-volatile memory 314 or the volatilememory (e.g., RAM) 315. The non-volatile memory 314 may be comprised of,e.g., flash memory for durably storing data, although the data may berewritten or erased at a later point in time. Preferably, the sampleperiod of the sensor 325 is programmable or adjustable, so that thesample period can be varied according to circumstances. The stored depthmeasurements, or a subset of stored depth measurements, can besubsequently read out from the non-volatile memory 314 or volatilememory 315, as the case may be, and transmitted, via the wirelesscommunication unit 310, to the remote monitoring station 170. Themonitoring device 300 can also periodically report its battery level tothe remote monitoring station 170.

In a preferred embodiment, the time interval(s) between samples taken bythe sensor 325 and the time interval(s) between data transmission fromthe monitoring device 300 to the remote monitoring station 170 areprogrammed through commands transmitted from the remote monitoringstation 170 to the monitoring device 300. The time intervals arepreferably stored, along with other operating parameters, in either thenon-volatile memory 314 or volatile memory 315 of the monitoring device300. Re-programming can be initiated in any of a variety of ways. Forexample, the remote monitoring station 170 may transmit a re-programmingcommand to the monitoring device 300, followed by an identification ofparameters to be altered, followed by the new parameter values. Theparticular format and protocol of the re-programming operation dependsupon the communication technique employed. The remote monitoring station170 may also re-program, through wireless commands transmitted to themonitoring device 170, parameters relating to any peripheral monitoringdevices, such as the time interval(s) between transmitting data from theperipheral monitoring devices to the remote monitoring station 170. Inone embodiment, the monitoring device 300 is configured to pass throughre-programming instructions to a specified peripheral monitoring devicethat can itself be remotely re-programmed.

The monitoring device 300 may also be configured to automatically adjustthe sample rate of water measurements obtained from the sensor 325without intervention needed by the remote monitoring station 170. Inthis embodiment, the monitoring device 300 is programmed with a numberof different alert levels, each of which corresponds to a specified(optionally programmable) sensor sample rate and/or data transmissionrate. As an example, the monitoring device 300 could be configured witha normal operating mode, a low alert operating mode, and a high alertoperating mode. The particular operating mode can be dictated by thedetected water level. The monitoring device 300 may ordinarily operatein the normal operating mode, wherein it may sample the depth (e.g.,water level) at a first rate (e.g., every 60 minutes). If the waterlevel exceeds a low alert threshold, then the monitoring device 300transitions to a low alert operating mode, and increases samplingfrequency to a second rate (e.g., every 20 minutes). When entering thelow alert operating mode, the monitoring device 300 may optionallytransmit a message to that effect to the remote monitoring station 170.If the water level then rises to an extent that it exceeds a high alertthreshold, the monitoring device 300 transitions to a high alertoperating mode, and increases sampling frequency to a third rate (e.g.,every 10 minutes). When entering the high alert operating mode, themonitoring device may optionally transmit a message to that effect tothe remote monitoring station 170.

The low alert threshold and high alert threshold may be pre-programmed,or may be programmed or re-programmed after installation of themonitoring device 300. The low alert and high alert thresholds may bebased in part on data collected during the initial period ofinstallation of the monitoring device 300.

The frequency with which data is transmitted from the monitoring device300 to the remote monitoring station 170 may also be varied dependingupon the operating mode. For example, in the normal operating mode, themonitoring device 300 may be programmed or configured to transmit dataat a first rate (e.g., once/week) to the remote operating station 170.In the low alert operating mode, the monitoring device 300 may beprogrammed to transmit data at a second rate (e.g., once/day). In thehigh alert operating mode, the monitoring device 300 may be programmedto transmit data at a third rate (e.g., once/hour).

The above sampling and broadcast rates are merely exemplary and are notintended to be limiting in any way. The actual sampling and broadcastrates may be selected based upon a number of factors, including thedesired level of scrutiny for the particular manhole, the amount ofavailable memory storage space to hold depth (e.g., water level)readings, and the need to preserve battery life to the maximum extentpossible. Likewise, the monitoring device 300 may have more or feweroperating modes, depending upon the particular needs of the monitoringsystem 100.

In addition to automatic transitioning between operating modes, themonitoring device 300 may also be forced to transition between operatingmodes by commands received from the remote monitoring station 170, ormay be programmed with override values for the sensor sampling intervaland reporting interval (as well as the low and high alert thresholdvalues). Alternatively, or in addition, the monitoring device 300,including its operating modes, can be programmable via one of the I/Oports 319. A benefit of remote programming of the sample and reportingintervals is that the monitoring device 300 may be manually set to morefrequent sampling or reporting rates during certain times such asperiods of bad weather (because of, e.g., possible rainwaterinfiltration) or local construction (which may cause obstructions,breaks, or leakages).

In a preferred embodiment, when reporting to the remote monitoringstation 170 in the normal course of operation, the monitoring device 300transmits a unique device identifier followed by the stored depth (e.g.,water level) measurements. The monitoring device 300 may also recordtimestamp data relating to the depth measurements as the readings aretaken, and transmit this information along with the stored depthmeasurements to the remote monitoring station 170. At the same time, orat other reporting intervals, the monitoring device 300 may alsotransmit data from any peripheral monitoring devices connected to it.When a water level reading exceeds an alert level (low or high), themonitoring device 300 preferably transmits immediately to the remotemonitoring station 170 the device identifier, water measurement readingvalue, and an alarm code indicating the nature of the alert. At the sametime, as noted above, the monitoring device 300 preferably enters analert mode wherein it takes more frequent water level readings and/orreports to the remote monitoring station 170 more frequently.

The remote monitoring station 170 preferably processes the data receivedfrom all of the monitoring devices 105 and centrally manages the overalloperation of the monitoring system 100. As previously indicated, theremote monitoring station 170 may transmit new operating parameters(including mode selections) to the various monitoring devices 105. Thenew operating parameters may, for example, by manually selected orentered by an administrator or operator via the user interface 173 atthe remote monitoring station 170. Upon receiving an alert or alarmmessage from any of the monitoring devices 105, the processing system172 may signal an operator or administrator by, e.g., activating adisplay light or audible alarm, and/or sending an electronic message(e.g., by e-mail or pager) or electronic facsimile communication toappropriate personnel. Historical data from the monitoring devices 105may be stored in the database 174 and analyzed for whatever desiredpurpose—e.g., hazard evaluation, growth planning, etc. The database 174may also correlate each device's unique identifier with its location,customer billing information (if applicable), and emergency handlingprocedure.

When an alert or alarm message is received by the remote monitoringstation 170, the processing system 172 or a manual operator may attemptto confirm the existence of a hazardous situation, or evaluate apossible cause thereof, by comparing the water level readings of themonitoring device 105 sending the alert or alarm with the readingsreceived from other monitoring devices 105 along the same pipeline(upstream or downstream). If those monitoring devices 105 are not yet attheir typical reporting period, the remote monitoring station 170,automatically or under manual control, can issue commands to the othermonitoring devices 105 to send their current water level readings to theremote monitoring station 170 for evaluation.

The remote monitoring station 170 may communicate with the variousmonitoring devices 105 according to any available and suitable wirelesscommunication technique. Preferably, the wireless communicationequipment on the monitoring device 105 and the wireless communicationtechnique are selected so as to provide adequate penetration through thesewer manhole cover 103, to allow proper monitoring of and communicationwith the installed monitoring device 105. In a particular embodiment,the monitoring device 105 communicates with the remote monitoringstation 170 using a suitable two-way pager communication protocol, suchas, for example, the Wireless Communications Transport Protocol (WCTP),which offers mechanisms for passing alphanumeric and binary messages.Two-way pager communication may be carried out over the ReFLEX™ network,which provides widespread geographical coverage of the United States, orany other available network. Communicating through a two-way pagernetwork may have the advantage of being less costly than, e.g.,communicating over a wireless cellular network.

In alternative embodiments, the monitoring devices 105 may communicatewith the remote monitoring station 170 through other types of wirelessnetworks, such as a cellular, PCS, or GSM wireless network, or throughany other type of wireless network. Communication may be conductedthrough base stations 152 (as illustrated in FIG. 1), and/or viacommunication satellites, and/or through wireless repeaters or relaystations. In remote locations, for example, where a monitoring device105 may not be near a wireless base station 152, a wireless repeater maybe positioned above ground near the manhole 108, to provide anintermediary link between the monitoring device 105 and the wirelessnetwork 150.

In some embodiments, messages transmitted wirelessly between themonitoring device 105 and the remote monitoring station 170 areformatted or exchanged according to a standard Internet protocol, suchas, for example, the Simple Mail Transport Protocol (SMTP), HyperTextTransfer Protocol (HTTP), or Transmission Control Protocol/InternetProtocol (TCP/IP). Scaled-down versions of these protocols may beutilized where certain functionality is not necessary for the purposesof the monitoring system 100.

Various features of a preferred monitoring device relate to means forsecuring the monitoring device to the interior of a manhole cavity. FIG.2, for example, illustrates in somewhat greater detail the positioningof a monitoring device 105 in a manhole 108. As shown in FIG. 2, amanhole 108 may have a manhole frame 109 abutting the ground surface,with a manhole cover 103 for providing access to the manhole cavity. Themanhole 108 may include a pre-cast cone-shaped housing 112, typicallyformed of concrete or a similar durable and relatively inexpensivematerial. One or more precast rings 110 may be interposed between themanhole frame 109 and the cone-shaped manhole housing 112. Preferably,the monitoring device 105 is mounted near the top of the manhole 108,within the area of the manhole frame 109 (if provided).

To facilitate rapid installation and removal of the monitoring device105, the monitoring device 105 is preferably suspended in the manhole bymultiple legs which emanate from the housing of the monitoring device105. FIG. 4A is a diagram illustrating a monitoring device 405 includinglegs 482 for mounting within a manhole frame 409. The internalfunctional features of the monitoring device 405 shown in FIG. 4A mayconform, for example, to those shown in FIG. 3 or FIG. 5. As illustratedin FIG. 4A, a set of legs 482 emanate from the housing 480 (depicted ina cylindrical shape) of the monitoring device 405, effectivelysuspending the monitoring device 405 at the top of the manhole cavity.The legs 482 may be formed, in whole or part, of a pliable, flexible orcompressible material, to allow the legs to adapt to the particularwidth across the manhole frame 409 (or the top of the manhole cavity, ifno manhole frame is present). Alternatively, the legs 482 may have arotatable screw member 487 for allowing adjustment of leg length, asillustrated in FIG. 4B, or a telescoping leg member. The legs 482 may beterminated in feet 483 which are preferably surfaced with an adhesive orgripping material to allow the legs to firmly grasp the inner surface ofthe manhole frame 409.

The number of legs 482 used to secure the monitoring device 405 to theinterior of the manhole may vary depending upon a number of factors.Generally, three or four legs 482 should be sufficient to secure themonitoring device 405. However, even a single leg can be used, if oneside of the housing 480 is in contact with the interior surface of themanhole frame 409. In such an embodiment, the contacting side of thedevice housing 480 may be surfaced with a gripping material such as softrubber or foam, for example. From a composition standpoint, it may bedesirable to manufacture the legs 482 from a non-metallic material, toavoid possible interference with wireless transmission or reception bythe monitoring device 405.

Installation of the monitoring device 405 shown in FIG. 4A may beconducted as follows. First, workers may remove or tilt open the manholecover, and then lower the monitoring device 405 into the manhole cavity.The monitoring device 405 may be tethered when lowering and installingit (or removing it), to prevent it from dropping to the bottom of themanhole cavity should it slip. Since the total span of a pair of legs482 may exceed the width of the manhole opening, the workers may need tobend or flex one or more legs 482, or, if having a rotatable screw ortelescoping member, retract one or more legs 482 when passing themonitoring device 405 through the manhole opening. Once inside themanhole frame 409 (or top of the manhole cavity), the legs may bereleased or extended and pressed against the inner surface of themanhole frame 409. The gripping feet 483 at the end of the legs 482 arepreferably used to secure the monitoring device 405 in position. Asnoted previously in connection with various other embodiments, themonitoring device 405 is preferably formed of a lightweight material andcomposed of lightweight components (e.g., low voltage battery,microcircuitry, etc.), and a benefit of such construction is that thedevice 405 can be more easily suspended with a mounting structure suchas illustrated in FIG. 4A. To remove the monitoring device 405, the legs482 are simply bent, flexed, or retracted, and the device 405 pulled upthrough the open manhole cover.

While no clamps or screws are necessary to secure the monitoring device405 in the above example, in alternative embodiments, screws, clamps,mounting brackets, or other means for securing the monitoring device 405may be utilized.

An advantage of various mounting structures and techniques describedabove is that the monitoring device 405 may be relatively simple andeasy to install or remove, even by unskilled workers, and generally doesnot require the use of tools nor the need to drill into the wall of themanhole. Also, the monitoring device 405 can be installed withoutnecessarily requiring workers to bodily enter the manhole enclosure,which can be advantageous in certain settings. For example, when aworker bodily enters a manhole enclosure, government regulations mayimpose special requirements, such as additional workers outside themanhole, the use of safety harness, an air supply, and so on, all ofwhich increases cost and time of installation or removal.

In the example shown in FIG. 4A, the monitoring device 405 has a whipantenna 406 that is partially located within the housing 480 andpartially extends atop the housing 480. The antenna 406 is preferablydirectional in nature, so as to maximize penetration through the manholecover. However, other antenna configurations may also be employed. Forexample, a small diameter hole may be drilled through the manhole cover,and an antenna extension placed through the small hole to provide betterwireless access. The tip of the antenna may be coated, glazed or sealedso that it lies flush with the surface of the manhole cover and isrelatively secure thereon. The antenna extension may be connected via acable or other means to the main housing 480 of the monitoring device405. In another embodiment, an antenna may be placed on the surface ofthe manhole, and magnetic coupling used to transmit signals from insidethe manhole through the externally located antenna. Other alternativeantenna arrangements may also be used.

FIGS. 6A and 6B are diagrams illustrating an example of one suchalternative antenna configuration. FIG. 6A shows an oblique view of amonitoring device 605 with an antenna piece 609 inserted into a hole inthe manhole cover 603, while FIG. 6B shows a cross-sectional view of theantenna piece 609 inserted in the hole 610 in the manhole cover 603. Thehole 610 may, for example, be counter-bored into the manhole cover 603to provide a suitable resting location for the antenna piece 609. Theantenna piece 609 may be of any size required to fit a suitable antennaarray 612 (for example, it may be approximately two inches across), andmay be any shape, although circular is preferred because of the abilityto fit it within a circular hole that can be readily created fromdrilling into the manhole cover 603. Alternative shapes include, forexample, a cone or funnel shape, or even a rectangular or polygonalshape where, for example, the manhole cover 603 has a pre-cast hole 610that does not require drilling in the field. The hole 610 may be createdfrom two drilling steps, a first step to bore a wide cylindrical insert,and a second step to bore a narrower hole through the base of thecylindrical insert, thus forming a lower lip 613 on which the antennapiece 609 can rest. Alternatively, a combined counter-bore drill bit maybe used to drill the hole 610 in a single step. Preferably, the hole 610is of a width such that the antenna piece 609 fits snugly therein, andthe antenna piece 609 can be secured by screws, epoxy, or other meansonce inserted in the hole 610.

The antenna piece 609 is preferably manufactured of durable, resilientmaterial such as plastic, that nevertheless allows for propagation ofwireless signals both upwards, outside of the manhole 608, and downwardstowards the monitoring device 605. Any of a variety of conventionalwireless repeater antennas may be used or adapted for the antenna array612 of the antenna piece 609; examples of conventional wireless repeaterantennas which propagate signals through glass or other dielectrics areknown, for example, in the automotive industry. The monitoring device605 preferably includes a separate antenna 606 which wirelessly couplesto the antenna array 612 within the antenna piece 609, to allow wirelesscommunication between the monitoring device 605 and a wireless basestation or network. The antenna piece 609 is preferably flush with thetop surface 618 of the manhole cover 603 to prevent it from interferingwith surface activity (for example, snow plow blades), but neverthelessshould have a clear “horizon” view for optimal wireless reception andtransmission. Likewise, the antenna piece 609 is preferably shaped suchthat it does not protrude from the bottom surface 619 of the manholecover 603, so that the manhole cover 603 can be easily dragged along theground without causing harm to the antenna piece 609. The antenna array612 may constitute, for example, a directional-type antenna, so thatloss of energy is minimized.

In certain embodiments, in order to provide as close proximity aspossible between coupled antenna elements, the antenna 606 connected tothe monitoring device 605 is formed as or contained within a springywire loop that touches or nearly touches the underside of the antennapiece 609. The flexibility of the antenna 606 in such an embodiment canhelp prevent damage when the manhole cover 603 is removed (since themanhole cover 603 is heavy, it may be swept across the manhole openingjust above the monitoring device 605).

FIG. 7 is a diagram illustrating another embodiment of a monitoringdevice 705 that may be of particular utility in situations whereobtaining a sufficiently clear signal path to a wireless network isotherwise difficult. The monitoring device 705 preferably has acylindrical body 781 terminated in a slightly wider cylindrical cap 782,to allow the monitoring device 705 to be securely inserted, in adrop-down fashion, into a counter-bored hole (similar to that describedwith respect to FIG. 6B) in a manhole cover 703. FIG. 8 illustrates howthe monitoring device 705 may be inserted into a counter-bored hole 710the manhole cover 703.

The monitoring device 705 preferably includes, encapsulated within thebody 781 and/or cap 782, the various internal components illustrated forthe monitoring device 300 in FIG. 3. However, the monitoring device 705may include additional or fewer components. The depth sensor 725 may bepositioned at the base of the body 781 to allow an unobstructed view ofthe floor of the manhole cavity. As is described in greater detail belowwith respect to FIG. 5, a second sensor 740 may optionally be positionedon the side of the housing 781 of the monitoring device 705, to detectif the manhole cover 703 (and thus the monitoring device 705) has beenremoved or otherwise moved from its ordinary resting position. Thesecond sensor 740 may alternatively be a pressure-type sensor that isplaced between the manhole cover 703 and the perimeter of the manholeopening, to detect if the manhole cover 703 is moved from its ordinaryresting position. An antenna (not explicitly shown in FIG. 7) may belocated in the cap 782 of the monitoring device 705, to provide anoptimum wireless signal path to remote wireless transmitters and/orreceivers. The antenna may be any compact type antenna having electricalcharacteristics suitable for communication in the intendedlocation/placement of the monitoring device 705. In certain embodiments,the antenna may be embedded in plastic to isolate it from the metal ofthe manhole cover 703. Since the monitoring device 705 has surfaceaccessibility, it may optionally be outfitted with, e.g., solar cells780 to allow re-charging of the battery during daylight operation.

An advantage of the configuration of the monitoring device 705 in FIG. 7is that it can be placed in a manhole cover 703 without the need toremove the manhole cover 703 (which can be a somewhat difficult tasksince manhole covers are fairly heavy and may be hard to dislodge dueto, e.g., accumulation of sediments, etc.). To facilitate placement ofthe monitoring device 703, a counter-bore hole can be drilled into themanhole cover 703, and the monitoring device 705 dropped into thecounter-bored hole and secured. The monitoring device 705 can be securedto the manhole cover 703 in any of a variety of ways. For example, itmay be bolted to the manhole cover 703 or otherwise locked into place.

In one embodiment, illustrated in FIG. 9, the monitoring device 905 issecured in place by a retaining ring 913. The retaining ring 913 may becompressed prior to being inserted into the hole just above the cap 982of the monitoring device, and then released so that it snaps out andconforms to the shape of a circular groove 914 surrounding the cap 982of the monitoring device 905. The spring-like action of the retainingring 913 serves to keep it locked in place. Retaining ring pliers may beused to facilitate removal of the retaining ring 913 and thus removal ofthe inserted monitoring device 905. In this particular embodiment, thecap 982 may be raised in the center to provide a flush surface with thetop surface 918 of the manhole cover 903.

The actual shape and dimensions of the monitoring device 705 may varydepending upon a number of factors. For example, it may, in certainsituations (especially, e.g., where peripheral monitoring devices arenot going to be used), be possible to fit all necessary electronics(including a battery/power supply) and sensor components in a housingroughly the size of the antenna piece 609 shown in FIG. 6, in which casethe monitoring device 705 may be approximately the size and shape of theupper cap 782 shown in FIG. 7. As another example, the upper cap 782and/or body 781 of the monitoring device 705 may be non-cylindrical inshape. As but one illustration, the manhole cover 703 may be cast with apre-fabricated square hole (with a protruding lower lip) into which asquare-shaped monitoring device 705 may be inserted. As anotherillustration, the upper cap 782 may be tapered (conical) orfunnel-shaped, and the hole may be of matching shape (either drilled onsite or pre-molded in the manhole cover 703). Of course, other shapesand sizes may be utilized. A cylindrical shaped monitoring device 705 ispreferred in those applications where pre-existing manholes may requiredrilling in order to retrofit with the monitoring device 705.

FIG. 5 is a block diagram illustrating an alternative embodiment of amonitoring device 500, as may be employed, for example, in themonitoring system 100 shown in FIG. 1, or other such systems. Amongother things, the monitoring device 500 shown in FIG. 5 provides somedegree tamper resistance with respect to the manhole 108 in which it isinstalled. In the example of FIG. 5, elements labeled with referencenumerals “5 xx” are generally similar to their counterparts labeled with“3 xx” in FIG. 3. However, the monitoring device 500 in FIG. 5 includessome additional features. The monitoring device 500 in FIG. 5 comprises,in addition to a first sensor 525 for taking depth measurements, asecond sensor 540 for detecting whether the manhole cover 103 has beentampered with. The second sensor 540 may be embodied, for example, as apressure sensor, with a pressure plate to be positioned such that if themanhole cover 103 is raised, the reduction in pressure will be detected.Alternatively, the second sensor 540 may be embodied as an optical(e.g., infrared) or ultrasonic detector, oriented upwards towards themanhole cover 103. The second sensor 540 may be initialized orcalibrated to the distance of the manhole cover 103. If the manholecover 103 is raised or removed, the second sensor 540 detects the changeand registers an alert or alarm condition. In such a case, themonitoring device 500 is preferably configured to transmit an alarmsignal indicating tampering to the remote monitoring station 170 toplace the appropriate personnel on notice.

If the second sensor 540 is required to sample periodically, theinterval between sample periods is preferably programmable or otherwiseselectable. The time between samples may, for example, be programmablevia wireless commands received from the remote monitoring station 170.The second sensor 540 might be commanded to sample more frequently priorto or during important events in the local area, such as a parade, etc.,where it may be considered important to ensure that manholes are notremoved or otherwise tampered with. Likewise, the monitoring device 500may be programmed to report back more frequently to the remotemonitoring station 170 during such events. The failure to receive anexpected reporting transmission at the remote monitoring station 170 ata particular time may result in an alarm or alert signal beinggenerating at the remote monitoring station 170, indicating themonitoring device 500 may have malfunctioned or else been tampered with.In the absence of extraordinary events, the sampling period may beselected so as to provide the desired level of security while at thesame time maximizing battery life.

In certain embodiments, the remote monitoring station 170 may, pursuantto programmed instructions or manual commands entered via the userinterface 173, transmit a status request signal to the monitoring device500, requesting verification that the manhole cover is in place. Uponreceiving such a status request signal, the monitoring device 500activates the second sensor 540, obtains a reading, and transmits theinformation back to the remote monitoring station 170. This operationallows greater flexibility in verifying the proper placement of manholecovers without necessarily having to increase the sampling/reportingrates of the second sensor 540 significantly, and can advantageously beused for test and verification purposes as well.

Alternatively, or in addition, a photocell sensor can be used in themonitoring device 500, to detect the presence of light entering themanhole (thereby indicating that the manhole cover has been removed orthat a source of light, such as a flashlight or lantern, is nearby).

In any of the various embodiments, a monitoring device may be outfittedwith a digital camera or other imaging device, and/or a microphone, forcollecting visual images and/or audio data which can be stored ortransmitted directly to the remote monitoring station. The visual oraudio data may be used to verify an alert condition, allow engineers orfield workers to make remote observations, or provide an additionallevel of security. The digital camera or imaging device, and/ormicrophone, may be integrated as part of the monitoring device, or elsemay be an external component connected to one of the monitoring device'sinput/output ports. FIG. 10 is a block diagram illustrating anembodiment of a monitoring device 1000, having a digital camera orimaging device 1050. In FIG. 10, components denoted with referencenumerals “10 xx” generally correspond to the similar components denotedwith reference numerals “3 xx in FIG. 3 or “5 xx” in FIG. 5. Themonitoring device 1000 illustrated in FIG. 10 thus may include a housing1005, a battery 1022, a processor 1012, a non-volatile memory portion1014, a volatile (RAM) memory portion 1015, various clocks and/or timers1017, one or more input/output (I/O) ports 1019 (which can optionally beconnected to various peripheral monitoring devices or instruments 1020),and a wireless communication unit 1010 coupled to an antenna 1006, allas previously described with respect to FIGS. 3 and 5. The monitoringdevice 1000 may also include a sensor 1025, such as an ultrasonicsensor, for measuring depth in the manhole as needed, and optionallyanother sensor 1040 which may be positioned so as to detect when themanhole cover 103 has been tampered with. The digital camera or imagingdevice 1050 may operate under control of the processor 1012, and may beinvoked at periodic intervals, upon detection of events by the primarysensor 1025 and/or second sensor 1040, or upon request from the remotemonitoring station 170. Likewise, a microphone 1055 may operate undercontrol of the processor 1012, and may be invoked at periodic intervals,upon detection of events by the primary sensor 1025 and/or second sensor1040, or upon request from the remote monitoring station 170.

The digital camera or imaging device 1050 may be oriented, for example,downwards to provide observation of the base of the manhole 108 or otherlocation, or upwards to provide observations of the manhole cover 103 orother features. The digital camera or imaging device 1050 may viewthrough a window 1051 (similar to window 1026 through which sensor 1025views) or else may, for example, be mounted to the exterior of themonitoring device 1000, or view through a fiber optic cable. The digitalcamera or imaging device 1050 may also share a common window with thesensor 1025. The digital camera or imaging device 1050 may also be usedto take an image of a meter within the manhole or other area. The imagecan then be transmitted back to the remote monitoring station 170, whereit may, if a visual meter reading, optionally be processed with opticalcharacter recognition (OCR) software to convert the image into anumerical value. A mirror (possibly movable) may be used to allow asingle digital camera or imaging device 1050 to view more than one area.The digital camera or imaging device 1050 may comprise, in one example,a CMOS image sensor, or else a CCD image sensor (which may use morepower, however, than a CMOS image sensor). The digital camera or imagingdevice 1050, and/or microphone 1055, may be remotely controlled throughthe remote monitoring station 170, and/or may be programmed to takeperiodic snapshots of visual or audio data according to a selectabletime schedule. The data may be stored in RAM 1015 or in non-volatilememory 1014 for later readout.

In certain environments, it may be advantageous for the monitoringsystem to include a local wireless relays in a distributed, self-formingwireless network which may provide, e.g., redundant communication pathsfor the various monitoring devices. Such a network may be referred to asa mesh network for its ability to form new communication paths and/orredundant communication paths, in a distributed fashion. FIG. 11 is ablock diagram of a portion of a monitoring system 1100 including amonitoring device 1105, which may sometimes be referred to herein as an“end node,” and a local wireless relay device 1145, which may sometimesbe referred to herein as a “street node.” The monitoring device 1105 maybe embodied as any of the monitoring devices as previously describedherein, such as those depicted for example in FIGS. 3, 5 or 10, and isgenerally positioned in a location for monitoring depth (e.g., waterlevel) such as in a manhole 1108, a storm drain, or other suitablelocation. The monitoring device 1105 preferably comprises a two-waywireless communication unit and antenna 1106 for communicating with thelocal relay device 1145. Likewise, the local wireless relay device 1145preferably comprises a two-way wireless communication unit and anantenna 1146 for communicating with the monitoring device 1105, and, incertain embodiments, with bridge nodes for conveying the monitored datato a remote monitoring station.

The local wireless relay device 1145 is ideally located in relativelyclose physical proximity to the monitoring device 1105—for example,attached or secured to a nearby telephone/utility pole or streetlamp1160—to minimize the distance that the RF signals from the monitoringdevice 1105 need to travel. The local wireless relay device 1145 mayhave an independent power source (e.g., battery), and/or mayadvantageously be connected to a power socket of the streetlamp 1160.Using the power socket of the streetlamp 1160 may significantly reducethe maintenance required for the overall monitoring system, and mayallow the local wireless relay device 1145 to communicate morefrequently without necessarily a concern for premature drain of thebattery. If a streetlamp 1160 is not in the vicinity of the monitoringdevice 1105, the local wireless relay device 1145 may alternatively beconnected to another continuous electrical power source that is in thearea (including drawing power from utility lines, if placed on a utilitypole), or else may rely on battery power.

The wireless communication unit 1107 of the monitoring device 1105 maybe embodied as a low power RF wireless device, such as a one-watt radiotransceiver, which transmits an RF signal through the manhole 1103 inorder to communicate with the local wireless relay device 1145, andlikewise receives an RF signal through the manhole 1103 from the localwireless relay device 1145. Similarly, the wireless communication unitof the local wireless relay device 1145 may be embodied as a low powerRF wireless device, such as a one-watt radio transceiver. In turn, thelocal wireless relay device 1145 may rebroadcast the informationreceived from the monitoring device 1105 to other local wireless relaydevices and eventually to the remote monitoring station, as will beexplained with respect to a more complete system as depicted in FIG. 13.The local wireless relay device 1145 may use the same radio transceiverto propagate data to other devices in the network, or may, if desired,use a different transceiver and different communication protocol.

FIG. 13 is a high-level diagram of a monitoring system 1300 utilizing,among other things, a plurality of local wireless relays to form, in oneaspect, a distributed, self-forming wireless network, according to apreferred embodiment as disclosed herein. In the example of FIG. 13, themonitoring system 1300 includes four different types of nodes, althoughin variations other types of nodes may be added, or some of the nodesmay be omitted. The nodes are arranged to communicate in a mesh network1320, which preferably acts as a distributed, self-forming andself-healing network allowing the monitoring devices 1305 to communicatevia redundant data paths to the remote monitoring station 1370. Themonitoring devices 1305, or end nodes, may be constructed, for example,according to any of the embodiments previously described herein. Themonitoring devices 1305 communicate with various other nodes of thedistributed mesh network 1320. In this particular example, the meshnetwork 1320 includes two different types of nodes—local wireless relaydevices 1322, or “street nodes” (as described with respect to FIG. 11),and bridge nodes (such as cellular gateway nodes 1324 or “sky nodes”).Examples of such devices are described hereinafter in connection withFIGS. 12A and 12B.

The monitoring devices 1305, or end nodes, each manage one or more datasensors and provides timing, control, data and programming storage, andwireless communication functions to allow remote monitoring of theactivity and operation of the monitoring devices 1305 by the remotemonitoring station 1370. The monitoring devices 1320 communicate withthe local wireless relay devices 1322, or street nodes, according totechniques generally described above with respect to FIG. 11. Once alocal wireless relay device 1322 receives information from a monitoringdevice 1305, and depending upon how often and under what circumstancesthe remote monitoring station 1370 needs to receive information, thelocal wireless relay device 1322 conveys the data through the meshnetwork 1320 until the data arrives at a bridge node, such as, forexample, a cellular gateway node 1324, or “sky node.” The cellulargateway node 1324 may then convey the data over a cellular network 1350to the remote monitoring station 1370. The remote monitoring station1370 may use the same communication path to send messages back to themonitoring devices 1305, for the purpose of, e.g., requesting additionalinformation (including from a different sensor, if provided) on themonitoring device), changing program parameters or the monitoring cycle,changing modes, modifying the instructions for the monitoring routine orother functions, or requesting some type of action.

In certain embodiments, in addition to or instead of using cellulargateway nodes 1324 as the bridge nodes, the mesh network 1320 mayinclude a bridge node 1360 that relies primarily on landlines 1361 forconveying data to the remote monitoring station 1370. The cellulargateway nodes 1324 may allow for increased flexibility in terms ofdeployment and regions of service, however.

While only a limited number of monitoring devices (i.e., end nodes)1305, local wireless relay devices (i.e., street nodes) 1322, and bridgenodes 1324, 1360 are depicted in FIG. 13 for purposes of illustration,the principles of FIG. 13 may be extrapolated to a mesh network 1320 ofarbitrarily large size, with an arbitrary number of nodes of each type.

According to one embodiment, the data carried by radio signals from amonitoring device 1305, or end node, to a local wireless relay device1322, or street node, can “mesh hop” to reach an available bridge node,such as a cellular gateway node (i.e., sky node) 1324. “Mesh hopping”permits data to find the most efficient path to a cellular gateway node(i.e., sky node) 1324 or other bridge node, and helps prevent data lossby providing redundant paths back to a central server or other computerat the remote monitoring station 1370. This network topology permitslarge scale installations where each monitoring device (end node) 1305generally communicates to a single local wireless relay device (streetnode) 1322, in a one-to-one fashion, but where the street nodes 1322 allcommunicate with one another and can pass data along to strategicallyplaced bridge nodes, such as cellular gateway nodes 1324 or other bridgenode 1360, which operate in a many-to-one mode. The street nodes 1322(and the bridge nodes 1324, 1360) may inter-communicate using anyavailable communication protocol, but preferably one that is relativelylow power, resistant to interference, and compatible with other wirelesscommunication systems as may geographically overlap the mesh network1320. For example, the street nodes may communicate using a spreadspectrum technique.

In the example in FIG. 13, the cellular gateway nodes 1324 or otherbridge node(s) 1360 preferably have the same basic capabilities as thelocal wireless relay devices 1322, and hence operate in one aspect as astreet or mesh node, but they also are capable of hand-shaking toanother form of network, such as a cellular network 1350 (whichtypically will be a publicly available network). The cellular gatewaynode 1324 may utilize, for example, a code-division multiple access(CDMA) or GSM transmission technique, or any other available technique,to communicate via cellular network 1350, according to the requirementsof the provider of the cellular network 1350. Data from the cellulargateway node 1324 is routed across the cellular network 1350 to theremote monitoring station 1370 where it may be, e.g., disseminated viaan Ethernet connection, and/or may be conveyed to a destination such asa PC or a database, so that the data can be properly stored and actedupon. Alternatively, the data may be transported over a landlineconnection 1361 via the bridge node 1360, and thus the remote monitoringstation 1370.

Mesh networking possesses several characteristics that result in anintelligent, self-forming and/or self-healing wireless network. Althoughin certain cases nodes may server different or overlapping functions, ingeneral the end node in the mesh network 1320 represents a terminationpoint where data is collected—i.e., the monitoring devices 1305 withbuilt-in sensor(s) to collect data. A mesh node is generally a node thatpasses along data to other mesh nodes, or to a bridge node. A bridgenode conveys data to a remote monitoring station, and/or bridges toanother type of network. According to one embodiment, the mesh network1320 self-forms by allowing individual local wireless relay devices(street nodes) 1322 and bridge nodes (such as cellular gateway nodes, orsky nodes 1324, or other bridge nodes 1360) to listen for, and associatethemselves, with the strongest signals emitted by the other nodes aroundthem in the mesh network 1320 to determine the ultimate routing pathsfor delivering the data. Thus, while various wireless communicationpaths are illustrated in basic example of the mesh network 1320 in FIG.13, over time those paths may change, and new paths may be established,either as environmental conditions change, nodes go off-line or areremoved, or new nodes are added. This type of operation results in a“mesh-like” network topology that may change from instance to instance,depending on the environment or data payload.

The mesh-like operation may be illustrated by way of example with thelayout in FIG. 13. There, data may be transported from the localwireless relay device (street node) 1322 at point “X” to a cellulargateway node (sky node) 1324 at point “Y” via two different data pathsdenoted “A” and “B” each utilizing different local wireless relaydevices 1322. Alternatively, and depending upon the conditions or theavailability status of the various other nodes in the mesh network 1320,the data may be transported via other local wireless relay devices 1322to a different cellular gateway node (sky node) 1324 at point “Z” shownin FIG. 13. Thus, particularly in a large network deployment, therewould be numerous alternative paths for conveying data from a particularmonitoring device (end node) 1305 to the remote monitoring station 1370,and those paths may dynamically change with time.

A variety of different communication protocols may be used within themesh network 1320. Nodes may associate or de-associate themselves withthe mesh network 1320 in a variety of different manners as well.According to one example, a node interacts with the mesh network 1320 bysending an association request to associate it with the mesh network1320, and then transmits data over the mesh network 1320 upon beingaccepted as part of the network. To initiate communication, a monitoringdevice 1305, or end node, may first detect the network presence (bylistening to communications occurring within the mesh network 1320), andthen send out an association request at a certain predetermined timewindow and/or at a certain time interval. The time interval can bepredetermined (e.g., every 5 minutes), or else may be trigged by anevent (such as, for example, when a sensor detects motion). The meshnodes listen for these association requests and, upon detection, sendthe detected association request along to the node's nearest bridge,such as a cellular gateway node 1324 or other bridge node 1360. Thecellular gateway node 1324 or other bridge node 1360 broadcasts signalsback through the various mesh nodes of the mesh network 1320 to the endnodes 1305, which creates a routing path for the data to travel upon.Each mesh node 1305 ranks the strength or quality of the routingresponses it observes from the various links, or “meshes,” and mayselect the best or highest quality link as its primary route, the secondhighest quality link as its secondary route, etc., and thereby forms therouting path. This process is repeated throughout the mesh network 1320,such that if a particular cluster of links are broken, the mesh nodesfind other paths to get the data to a live bridge node 1324 or 1360 by,e.g., using their second or third choice routes.

In certain embodiments, the individual nodes of the mesh network 1320may use a frequency hopping technology that allows the nodes tocommunicate over different frequencies at different times, therebypotentially minimizing interference from other networks thatgeographically overlap with the mesh network 1320. For example, thestreet nodes 1322 and bridge nodes 1324, 1360 may employ afrequency-hopping spread spectrum (FHSS) technique, or else mayperiodically switch communications to different frequencies in anattempt to reduce interference, particularly if all of the incomingsignals are weak or have errors.

The fact that the mesh nodes generally will be regularly be listeningfor communications from other mesh nodes, or end nodes, can be taxingfrom a power consumption perspective, and may be a consideration indesigning the scalability of mesh. FIG. 14 is a timing diagramillustrating one possible protocol by which a measure of powerconservation may be achieved. In FIG. 14, a repeating time window isused to define time periods when a monitoring station may be active fortransmitting event data and listening for responses or other informationfrom the mesh network 1320. Monitoring devices 1305 may staysynchronized by listening, for example, for a periodic time marker thatis propagated from a central location in the mesh network 1320 via thelocal wireless relay units 1322. In this example, shown from theperspective of a local wireless relay unit 1322, a repeating time window1405 is divided into a listening period 1408 in which monitoring devices1305 generally transmit to the local wireless relay unit 1322, and aresponse/transmit period 1409 during which the local wireless relay unit1322 transmits or otherwise responds to the monitoring devices 1305.This timing structure allows the monitoring units 1305 to remain“asleep” during designated time periods, thereby conserving batterypower. The local wireless relay unit 1322 may also remain in a sleepstate during periods where it does not expect to receive transmissions.The frequency of the time window 1405 may vary depending upon, e.g., thealert stage of the overall system or a particular monitoring device1305. In terms of communicating with other mesh nodes, the localwireless relay unit 1322 may transmit or receive data during a differenttime window (not shown in FIG. 14) reserved for communication among themesh nodes.

FIG. 14 further illustrates an association request 1421 transmitted in alistening period 1408 of the time window 1405 from a monitoring device1305 to a local wireless relay unit 1322. The association request 1421indicates the desire of the monitoring device 1305 to associate itselfwith the mesh network 1320. The local wireless relay units 1322 listenfor these association requests and, upon detection, send the detectedassociation request along to the nearest bridge, such as a cellulargateway node 1324 or other bridge node 1360. At some later point, thelocal wireless relay unit 1322 receives an acknowledgment from thebridge, and conveys an association acknowledgment message 1422 to themonitoring device 1305 during the response/transmit period 1409 of asubsequent time window 1405. Thereafter, the monitoring device 1305 maysend data to the local wireless relay device 1322 and receive data orother information in return, during subsequent time windows 1405.

Although in a preferred embodiment a local wireless relay device 1322associates with a single monitoring device 1305, in other embodiments alocal wireless relay device 1322 may associate with multiple monitoringdevices 1305. The local wireless relay device 1322 may accomplishmultiple association by, e.g., establishing different time windows forcommunicating with the different monitoring devices 1305.

The particular architecture of the mesh network 1320 provides it withthe ability to utilize or be maintained over a large variety of wiredand wireless formats including, for example, 900 Mhz radio, 2.4 Ghzradio, CDMA cellular, GSM/GPRS cellular, Ethernet cable, ISDN cable,serial cable, or others. Using TCP/IP at the bridge/gateway level, themesh network 1320 may allow ready integration with new wireless formatsas technology becomes available; for example, it may be adaptable toWiMax radio, which has recently been publicized but is not yetcommercially available. Similarly, reporting to end users from theremote monitoring center 1370 can be made essentially platform agnostic,by relying upon a SQL (Structured Query Language) database which candynamically push and pull the data into multiple formats (e.g.voice/phone, website, SMS, email, etc.).

The various nodes in the mesh network 1320 may pass along informationconcerning the frequency, reliability, and other statistical oranalytical information concerning node inter-communications to theremote monitoring station 1370, which may maintain, for example, thenumber of readings received and number of packets forwarded by eachnode. Reports may be generated for operators at the remote monitoringstation 1370 to assess the status of the mesh network 1320. Thisinformation may allow the operators to, for example, recommend addingnew local wireless relay devices 1322 or bridge nodes 1324, 1360 to themesh network 1320, or changing the location of certain nodes, or makingother adjustments as may be necessary to improve communications withinthe mesh network 1320. The mesh network 1320 also has the ability, viathe remote monitoring center 1370 or otherwise, to remotely updatefirmware on each of the mesh nodes, to permit for example new softwarefunctionality to be introduced remotely and to assist in networkmanagement and improvement.

FIG. 12A is a block diagram of an embodiment of a local wireless relaydevice 1200 as may be used as a “street node” in, for example, themonitoring system of FIG. 13. In FIG. 12A, the local wireless device1200 comprises a wireless communication unit 1210 which is responsiblefor communicating with both monitoring devices (e.g., 1305 in FIG. 13)and other street or mesh nodes. The wireless communication unit 1210 mayutilize any suitable wireless protocol and, in certain embodiments, maybe embodied as multiple radio units if different wireless protocols areused by the different nodes in the mesh network 1320. If embodied as asingle RF radio, the wireless communication unit 1210 may communicatewith a monitoring device 1305 during one time window and other meshnodes in another time window. The wireless communication unit 1210 isconnected to an antenna 1206, and operates under control of a processor1212 (which may comprise, e.g., a microprocessor, microcomputer, ordigital circuitry) for controlling the basic functions of the localwireless relay device 1200. The processor 1212 preferably has access toa local memory 1214, which may, e.g., store programming instructions forexecution by the processor 1212, operational parameters, and data beingrelayed over the mesh network 1320. The local memory 1214 may be usedfor storing a mesh link table 1235 which ranks local signals from othernodes according to any available metrics such as strength (e.g.,received signal strength indication (RSSI)), signal-to-noise level,error level, and/or quality. The rankings in the mesh link table 1235may be used by the local wireless relay device 1200 to select theprimary route, secondary route, and so on, as previously described. Theprocessor 1212 may also may have access to various clocks and/or timers1217 for carrying out timing of certain events (e.g., timing ofintervals between data transmissions). The local wireless relay device1200 includes an external power supply input block 1222 connected to anexternal power source, such as a power socket on a utility pole orstreetlamp. The local wireless relay device 1200 may have a batterybackup and, in certain embodiments, rely upon battery, solar, or otherpower sources.

FIG. 12B is a block diagram of an embodiment of a cellular gateway node1250 as may be used as a “sky node” in, for example, the monitoringsystem of FIG. 13. The cellular gateway node 1250 in FIG. 12B is similarin many basic respects to the local wireless relay device 1200, andcomprises, for example, a processor 1262, a local memory 1264 (includinga mesh link table 1285), various clocks and/or timers 1267, and anexternal power supply input block 1272, all serving generally the samepurpose as the corresponding components in the local wireless relaydevice. Because the cellular gateway node 1250 interfaces with a secondwireless (e.g., cellular) network 1350, the processor 1262 also managesthe interactions with that network as well as the nodes of the meshnetwork 1320. Preferably, the cellular gateway node 1250 includes awireless communication unit 1260 and antenna 1266 that are similar tothe corresponding components of the local wireless relay unit 1200, forcommunicating within the mesh network 1320, as well as a second wirelessunit 1270, such as a cellular transceiver, for communicating over thesecond wireless (e.g., cellular) network 1350. Using this configuration,the cellular gateway node 1250 may communicate simultaneously within themesh network 1320 and over the cellular network 1350. The cellulargateway node 1250 may convert data received from the mesh network 1320into a different format, such as TCP/IP format, used for backhaultransport to the remote monitoring station 1370.

In any of the embodiments described herein, a monitoring device or otherdevice may use multiple (e.g., four) batteries in connection with aswitching methodology to extend battery power. The battery controlsystem for the monitoring devices, or end nodes, may periodically rotatethe batteries so that only one of the multiple batteries is active at atime (or more if multiple batteries are needed for regular operation) oras each battery drains to below a critical level. To accomplish this,the monitoring device may include circuitry for periodically measuringthe remaining battery voltage and for conveying this information to thedevice processor or controller, and circuitry for switching power supplyconnections from one battery to another. The effective battery life forthe monitoring device becomes the cumulative battery life for eachbattery (or set of batteries), and the longevity of the monitoringdevice may thus be significantly increased before battery replacement isrequired.

In any of the monitoring systems described herein, a particular type ofmonitoring device may be used exclusively, or else a combination ofdifferent monitoring devices may be used. For example, an in-holemonitoring device (such as illustrated, e.g., in FIG. 6A) may be used inlocations where a sufficiently clear communication channel is available,and a surface-accessible monitoring device (such as illustrated, e.g.,in FIG. 7) may be used in locations where it is difficult to obtain asufficiently clear communication channel using an in-hole monitoringdevice. Similarly, monitoring devices connected to the monitoringstation by landlines may be used in combination with wireless monitoringdevices, in connection with an integrated monitoring system having bothwired and wireless monitoring devices.

With any of the monitoring devices described herein, a selection ofdifferent types of wireless communication may be provided. According toone technique, for example, the specific wireless circuitry is selectedat the time of installation. Field workers may test a number ofdifferent types of wireless equipment at an installation site, andselect the one with optimal reception (e.g., signal strength). Themonitoring device may be configured such that a small module (e.g.,circuit board, electronic chip, or other type of module) containing theappropriate wireless circuitry may be inserted into the monitoringdevice prior to installation. Different monitoring devices may thereforeutilize different types of wireless communications, and differentwireless providers, to communicate with the remote monitoring station.According to an alternative technique, several different types ofwireless circuitry are included in the same monitoring device, and aswitch provided on the monitoring device is used to select which type ofwireless circuitry to utilize.

While various components are described in certain embodiments as being“connected” to one another, it should be understood that such languageencompasses any type of communication or transference of data, whetheror not the components are actually physically connected to one another,or else whether intervening elements are present. It will be understoodthat various additional circuit or system components may be addedwithout departing from teachings provided herein.

Implementation of one or more embodiments as disclosed herein may leadto various benefits and advantages. For example, a monitoring system inaccordance with certain embodiments as disclosed herein may providesanitary wastewater system owners and/or operators with an early warningof possible overflow conditions at specifically monitored manhole orother locations, thus allowing the owner/operators sufficient time toprevent actual overflow by cleaning, servicing, shutoff, or othermeasures. Overflow prevention reduces the risk of costly cleanupoperations, health hazards and environmental damage, interruption inservice, and penalties from regulatory authorities or agencies. Otherpotential benefits of various monitoring systems as disclosed hereininclude reduction of routine preventative pipe cleaning and itsassociated costs, sewer system historical data for growth planning, andgross rainwater infiltration measurements.

While various systems and devices disclosed herein have most often beendescribed in the particular context of monitoring, it will be understoodthat the techniques and principles disclosed may be applicable oradapted to other situations wherein it may be necessary or desirable tomonitor the level of water, liquid, or any other time of substance thatcan accumulate over time. For example, monitoring systems as disclosedherein may be applicable to measuring and monitoring any type of waterbody (such as rivers, lakes, or coastal waters), or any type of liquidin an open pipe setting, or any other type of measurable matter (e.g.,sand, ore, silt, mud, etc.) that accumulates.

While preferred embodiments of the invention have been described herein,many variations are possible which remain within the concept and scopeof the invention. Such variations would become clear to one of ordinaryskill in the art after inspection of the specification and the drawings.The invention therefore is not to be restricted except within the spiritand scope of any appended claims.

1. A monitoring system, comprising: a plurality of monitoring devicesdisposed in sewer manholes, each of said monitoring devices comprising(i) a sensor configured to obtain depth measurements at periodicintervals, and (ii) a wireless transceiver; a plurality of wireless meshnodes arranged in a distributed network, at least one of said mesh nodesin physical proximity to each of said monitoring devices forcommunicating wirelessly therewith, wherein at least some of said meshnodes communicating with said monitoring devices are also configured towirelessly communicate with one another; and at least one bridge nodeconfigured to communicate wirelessly with said mesh nodes, and totransfer information between said mesh nodes and a remote monitoringstation; wherein said mesh nodes each comprise a wireless transceiverconfigured to communicate with other mesh nodes, at least one of saidmonitoring devices, and said bridge node, according to a multiplexingtechnique; wherein said mesh nodes convey depth measurement data fromthe monitoring devices to the remote monitoring station, and conveyinstructions or other information from the remote monitoring station tothe monitoring devices; and wherein said bridge node comprises a firstwireless transceiver for communicating with the mesh nodes according toa first protocol, and a gateway interface for communicating with saidremote monitoring station via a second network.
 2. The monitoring systemof claim 1, wherein said mesh nodes are configured to provide multiplealternative communication paths from individual monitoring devices tosaid bridge node, each of said alternative communication paths from anindividual monitoring device involving a different combination of meshnodes.
 3. The monitoring system of claim 2, wherein said mesh nodesmeasure and store signal strength and/or quality metrics with respect toother mesh nodes, and select a communication path to one of the othermesh nodes based thereon.
 4. The monitoring system of claim 1, wherein afirst one of said mesh nodes in direct wireless communication with afirst one of said monitoring devices is configured to relay messagesfrom a second one of said mesh nodes in direct wireless communicationwith a second one of said monitoring devices to said bridge node, and torelay return path messages from said bridge node to the second one ofsaid mesh nodes.
 5. The monitoring system of claim 1, wherein saidsecond network comprises a wireless network, and wherein said gatewayinterface comprises a second wireless transceiver for communicating withsaid remote monitoring station, said second wireless transceiveroperating according to a different protocol than said first wirelesstransceiver.
 6. The monitoring system of claim 5, wherein said wirelessnetwork comprises a cellular network, and wherein said second wirelesstransceiver operates according to a cellular telephone protocol.
 7. Themonitoring system of claim 1, wherein at least some of said mesh nodesare configured to be mounted on a utility pole.
 8. The monitoring systemof claim 7, wherein the mesh nodes mounted on a utility pole areconfigured to draw power directly from a power socket on the utilitypole.
 9. The monitoring system of claim 1, wherein said monitoringdevices initially associate with the distributed network by transmittingan association request message, and receiving an acknowledgment message.10. The monitoring system of claim 1, wherein said monitoring devicescomprise multiple sensors monitoring different aspects of the sewermanhole, and are configured to transmit data obtained from said multiplesensors to the mesh nodes of said distributed network.
 11. A method formonitoring a plurality of sewer manholes distributed over a largegeographic region, comprising: placing a plurality of monitoring devicesin sewer manholes, each of said monitoring devices comprising (i) asensor configured to obtain depth measurements at periodic intervals,and (ii) a wireless transceiver; disposing a plurality of wireless meshnodes throughout a geographic region encompassing the sewer manholes, atleast one of said mesh nodes in physical proximity to each of saidmonitoring devices for communicating wirelessly therewith and at leastsome of said mesh nodes communicating with said monitoring devicesconfigured to also wirelessly communicate with one another, therebyforming a distributed mesh network; disposing at least one bridge nodein the distributed mesh network, said bridge node configured tocommunicate wirelessly with said mesh nodes; conveying depth measurementdata from said monitoring devices to a remote monitoring station via aplurality of communication paths including said mesh nodes and saidbridge node of the distributed mesh network; conveying information fromsaid remote monitoring station to said monitoring devices, via said meshnodes and said bridge node of the distributed mesh network; conveyinginformation from the monitoring devices to the remote monitoring stationvia said mesh nodes, and conveying instructions or other informationfrom the remote monitoring station to the monitoring devices via saidmesh node; wherein a first one of said mesh nodes in direct wirelesscommunication with a first one of said monitoring devices relaysmessages from a second one of said mesh nodes in direct wirelesscommunication with a second one of said monitoring devices to saidbridge node, and relay return path messages from said bridge node to thesecond one of said mesh nodes; and wherein said bridge node comprises afirst wireless transceiver for communicating with the mesh nodesaccording to a first protocol, and a gateway interface for communicatingwith said remote monitoring station via a second network.
 12. The methodof claim 11, wherein said mesh nodes dynamically select saidcommunication paths based upon the signal strength and/or quality of thesignals received at said mesh nodes.
 13. The method of claim 11, whereinsaid mesh nodes provide multiple alternative communication paths fromindividual monitoring devices to said bridge node, each of saidalternative communication paths from an individual monitoring deviceinvolving a different combination of mesh nodes.
 14. The method of claim11, wherein at least one mesh node utilizes the same wirelesstransceiver to communicate with other mesh nodes, one of the monitoringdevices, and said bridge node, according to a multiplexing technique.15. The method of claim 14, wherein said mesh nodes measure and storesignal strength and/or quality metrics with respect to other mesh nodes,and select a communication path to one of the other mesh nodes basedthereon.
 16. The method of claim 11, wherein said second networkcomprises a wireless network, and wherein said gateway interfacecomprises a second wireless transceiver for communicating with saidremote monitoring station, said second wireless transceiver operatingaccording to a different protocol than said first wireless transceiver.17. The method of claim 16, wherein said wireless network comprises acellular network, said method further comprising the step of operatingsaid second wireless transceiver according to a cellular telephoneprotocol.
 18. The method of claim 11, further comprising the step ofmounting a plurality of said mesh nodes on utility poles.
 19. The methodof claim 18, further comprising the step of providing power from saidutility poles to the mesh nodes mounted thereon, by drawing powerdirectly from a power socket on the utility pole.
 20. The method ofclaim 11, further comprising the step of initially registering saidmonitoring devices with the distributed network by transmitting anassociation request message from a monitoring device desiring toassociate with the distributed network, and receiving an acknowledgmentmessage at the monitoring device in return.
 21. A method for monitoringa plurality of depth measurement devices distributed over a geographicregion, comprising: disposing a plurality of stationary monitoringdevices in different geographic locations, each of said monitoringdevices comprising (i) a sensor configured to obtain depth measurementsat periodic intervals, and (ii) a wireless transceiver; disposing aplurality of stationary mesh nodes throughout the geographic region,said mesh nodes configured to communicate wirelessly with saidmonitoring devices using a low power radio frequency (RF) communicationtechnique and to communicate wirelessly to each of the other mesh nodeswithin range, thereby forming a distributed mesh network; disposing atleast one bridge node in the distributed mesh network, said bridge nodeconfigured to communicate wirelessly with said mesh nodes; conveyingdepth measurement data from said monitoring devices to a remotemonitoring station via said bridge node, across a plurality ofcommunication paths dynamically selected by said mesh nodes, at leastone of the selectable communication paths including a plurality of saidmesh nodes; conveying information from said remote monitoring station tosaid monitoring devices via the distributed mesh network; conveyinginformation from the monitoring devices to the remote monitoring stationvia said mesh nodes, and conveying instructions or other informationfrom the remote monitoring station to the monitoring devices via saidmesh nodes; wherein a first one of said mesh nodes in direct wirelesscommunication with a first one of said monitoring devices relaysmessages from a second one of said mesh nodes in direct wirelesscommunication with a second one of said monitoring devices to saidbridge node, and relay return path messages from said bridge node to thesecond one of said mesh nodes; and wherein said bridge node comprises afirst wireless transceiver for communicating with the mesh nodesaccording to a first protocol, and a gateway interface for communicatingwith said remote monitoring station via a second network.
 22. The methodof claim 21, further comprising the step of disposing said monitoringdevices in sewer manholes spread over the geographic region.
 23. Themethod of claim 21, wherein said mesh nodes dynamically select saidcommunication paths based upon the signal strength and/or quality of thesignals received at said mesh nodes.
 24. The method of claim 23, whereinsaid mesh nodes provide multiple alternative communication paths fromindividual monitoring devices to said bridge node, each of saidalternative communication paths from an individual monitoring deviceinvolving a different combination of mesh nodes.
 25. The method of claim24, said mesh nodes each utilize a single wireless transceiver toalternate communications with other mesh nodes, with one of themonitoring devices, and with said bridge node, according to amultiplexing technique.
 26. A monitoring system for monitoring aplurality of depth measurement devices distributed over a geographicregion, comprising: a plurality of wireless mesh nodes arranged in adistributed network, a subset of said wireless mesh nodes each locatedin physical proximity to one of a plurality of wireless depth monitoringdevices configured to obtain depth measurements at periodic intervals;and at least one bridge node configured to communicate with saidwireless mesh nodes, and to transfer information between said wirelessmesh nodes and a remote monitoring station; wherein said wireless meshnodes, including said subset of wireless mesh nodes, are configured towirelessly communicate with one another to facilitate conveyance of datafrom the depth monitoring devices to said bridge node; wherein saidwireless mesh nodes provide multiple alternative communication pathsfrom individual depth monitoring devices to said bridge node, each ofsaid alternative communication paths from an individual depth monitoringdevice involving a different combination of mesh nodes; whereby selecteddepth measurements from said wireless depth monitoring devices areconveyed to said remote monitoring station; and wherein said bridge nodecomprises a first wireless transceiver for communicating with thewireless mesh nodes according to a first protocol, and a gatewayinterface for communicating with said remote monitoring station via asecond network.
 27. The monitoring system of claim 26, wherein each ofsaid subset of wireless mesh nodes utilizes the same wirelesstransceiver for alternating communications with other wireless meshnodes, with a locally proximate one of the depth monitoring devices, andwith said bridge node, according to a multiplexing technique.
 28. Themonitoring system of claim 26, wherein said wireless mesh nodes measureand store signal strength and/or quality metrics based on signalsreceived from other nodes, and select a communication path basedthereon.
 29. The monitoring system of claim 26, wherein said secondnetwork comprises a wireless network, and wherein said gateway interfacecomprises a second wireless transceiver for communicating with saidremote monitoring station, said second wireless transceiver operatingaccording to a different protocol than said first wireless transceiver.30. The monitoring system of claim 29, wherein said wireless networkcomprises a cellular network, and wherein said second wirelesstransceiver operates according to a cellular telephone protocol.
 31. Themonitoring system of claim 26, wherein said monitoring devices aredisposed in a plurality of sewer manholes over the geographic region.32. The monitoring system of claim 31, wherein a plurality of thewireless mesh nodes in said subset of wireless mesh nodes are configuredto be mounted on utility poles and draw power directly therefrom.